It is advantageous to know the quality of a recording medium, for example, an optical disc such as a CD, DVD+, DVD-, DVD-RAM, HD-DVD, Blu-ray disc or the like. A method to know the disc quality well is to obtain the number and distribution of errors in the disc. From error analysis, errors due to a recording apparatus or the disc per se can be distinguished. The respective manufacturers of the recording apparatus and the disc can improve their products according to result of the error analysis.
Generally, when an optical disc is read by a disc drive, a kind of errors so called “burst errors” in the present invention are essentially caused by defects of the disc per se. In contrast, another kind of errors so called “random errors” are mainly caused by the recording apparatus. For monitoring the recording or writing quality, it is necessary to omit the burst errors due to the inherent disc defects when calculating the total errors.
An erroneous byte is a data byte in which at least one bit is of a wrong value. An error burst is defined as a sequence of bytes in which there are not more than a predetermined number m (m=2 in a usual case) correct bytes between any two erroneous bytes. A length of the error burst is defined as the total number of bytes counted from a first erroneous byte separated by a series of continuous correct bytes, which has at least m+1 (3 in a usual case) correct bytes to a final erroneous byte also separated by at least m+1 (3 in a usual case) continuous correct bytes. FIG. 1 is a diagram schematically illustrating an example of an error burst of an optical disc. In this example, the length of the error burst is 10 bytes. In addition, the number of the erroneous bytes in this error burst is 7.
An error burst of a length longer than or equal to n (n=40 in a usual case) bytes can be referred to a burst error. On the other hand, an error burst of a length less than 40 bytes is referred to a random error. There is a need for a method to obtain information of the different types of errors during data reproduction. The error profile such as the numbers and distribution of different types of errors including burst errors and random errors can be used to estimate the recording or writing quality or other applications.